The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention relates to encapsulated toner compositions comprised of a core comprised of a polymer binder, a nonvolatile organic liquid, and pigment, and a polymeric shell thereover prepared by interfacial polymerization in embodiments. The aforementioned polymeric shell, which in embodiments can comprise a polyether-urea material, possesses in many instances low permeability characteristics, and thus enables effective containment of the core components. The presence of a soft, flexible moiety such as a polyether segment in the shell polymer can improve the packing of the shell polymer in the shell structure. Proper packing of the shell polymers permits, for example, a high density shell structure, and lowers, suppresses, or in some instances may eliminate the shell's permeability thereof, especially to low molecular weight core components such as the core polymer binder and the nonvolatile organic liquid. A high degree of shell permeability can cause the undesirable loss of core components, particularly the aforementioned organic liquid, and thus drastically degrade the toner's properties. Another associated problem of shell permeability relates to the leaching of core binder to the toner's surface, and the associated problems of toner agglomeration or toner blocking, as well as image ghosting in imaging and printing processes, which problems are avoided or minimized with the toners of the present invention. A specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core of a thermoplastic polymer, or plurality of polymers, binder, a nonvolatile organic liquid, and a magnetic pigment, and wherein the core is encapsulated within a polymer shell, such as polyether-urea shell, which toner has a number of advantages including, for example, the elimination or minimization of pen print-through associated with some prior art toners which have soft core polymer binders with low softening and glass transition temperatures. Other advantages of the toner compositions of the present invention in embodiments thereof include excellent toner fixing properties, excellent image visual quality and permanence, the absence or minimization of toner agglomeration, the absence or minimization of image ghosting, and retention of the core components. Another specific embodiment of the present invention relates to a pressure fixable encapsulated toner composition wherein the shell is comprised of the reaction product of a mixture of a polyether-based isocyanate or isocyanates and a polyisocyanate monomer or monomers selected, for example, from the group consisting of benzene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, polymethylene diisocyanate, and the like, with a polyamine or polyamines. In another embodiment of the present invention, the toner compositions obtained can include thereon an electroconductive material, such as carbon black, graphite, and the like, thereby enabling compositions with a controlled and stable volume resistivity such as, for example, from about 1.times.10.sup.3 to about 1.times.10.sup.8 ohm-cm, and preferably from about 1.times.10.sup.4 and 1.times.10.sup.6 ohm-cm, which toners can be particularly useful for inductive single component development processes.
Examples of advantages associated with the toner compositions of the present invention in embodiments thereof are as indicated herein, and include the elimination and/or the minimization of image ghosting, excellent fixing characteristics, excellent image visual quality and very acceptable image permanence, acceptable surface release properties, in some instances, enabling their selection, for example, in imaging systems wherein a release fluid such as a silicone oil is avoided, substantially no toner agglomeration, acceptable powder flow characteristics, and minimal or no leaching or loss of the core components. Also, the toners of the present invention in embodiments thereof possess the advantages of the ability to provide a substantially higher image fix to plain paper, and in some instances, image fix levels equivalent to those of heat fused images; a shell with substantially improved mechanical properties; and moreover, the shell precursors selected possess in many instances low vapor pressures, thus reducing environment hazards. Further, with the toner compositions of the present invention in embodiments thereof, the shell does not rupture prematurely causing the core component comprised, for example, of a polymer binder and magnetite, or other pigment to become exposed, which upon contact with other toner particles or toner development subsystem component surfaces and the like forms undesirable agglomerates. The excellent surface release properties possessed by the toners of the present invention in embodiments thereof also provide for a complete or substantially complete transfer of toned images to a paper substrate during the development process. Furthermore, the toner compositions of the present invention can be obtained in high reaction yields in several embodiments thereof as the process of preparation thereof can involve a simple washing and sieving procedure to remove the coarse and fine particles in place of the conventional costly particle size classification procedure, thus dramatically lowering the manufacturing cost thereof. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In embodiments, the toner compositions of the present invention can be selected for pressure fixing processes for ionographic printing wherein dielectric receivers, such as silicon carbide, are utilized, reference U.S. Pat. No. 4,885,220 , the disclosure of which is totally incorporated herein by reference. Specifically, the toner compositions of the present invention can be selected for image development in commercial Delphax printers such as the Delphax S9000, S6000, S4500, S3000, and Xerox Corporation printers such as the 4060.TM. and 4075.TM., wherein, for example, transfixing is utilized, that is the transfer and fixing of the toned image from the dielectric receiver onto a paper substrate is accomplished simultaneously in one single step with pressure, with an image fix of at least 80 percent in an embodiment of the present invention. Another application of the toner compositions of the present invention is for two component development systems wherein, for example, the image toning and transfer is accomplished electrostatically, and the fixing of the transferred image is achieved by application of pressure, with or without the assistance of thermal energy.
The toner compositions of the present invention can, in one specific embodiment, be prepared by interfacial polymerization involving microcapsule shell-forming polycondensation, followed by in situ core polymer binder forming free radical polymerization of a core monomer or monomers in the presence of a free radical initiator. In a process embodiment of the present invention, the encapsulated toner can be prepared without using organic solvents as diluents or reaction media, thus eliminating, for example, explosion hazards associated therewith; and furthermore, these processes can be accomplished without expensive and hazardous solvent separation and recovery steps. Moreover, with the process of the present invention there are obtained in some instances improved toner throughput yield per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by the nonvolatile organic liquid, the liquid core monomer(s) and shell precursor(s). The toners prepared in accordance with the process of the present invention are useful for permitting the development of images in reprographic imaging systems, inclusive of electrostatographic and ionographic imaging processes wherein pressure fixing is selected, and for other imaging and printing processes.
The toner compositions of the present invention can contain unique shell materials that permit the containment or substantial retention of the core components, thus eliminating or substantially suppressing core binder and organic liquid diffusion and leaching. As a consequence, the problems of toner agglomeration and image ghosting can be completely or substantially eliminated. Furthermore, the toner compositions of the present invention dramatically improve the efficiency of the image transfer process to substrates, such as paper, in many embodiments. Also, with the toner compositions of the present invention, particularly with respect to their selection for inductive single component development processes, the toner particles can contain on their surfaces a uniform and substantially permanently attached electroconductive material, thereby imparting certain stable electroconductive characteristics to the particles inclusive of situations wherein these particles are subjected to vigorous agitation. With some of the prior art encapsulated toners, the surface conductivity properties of the toner particles may be unstable when subjected to agitation, especially for example when electroconductive dry surface additives, such as carbon black, are selected. Further, with the aforementioned prior art toner compositions there are usually obtained images of low image quality with substantial background deposits, particularly after a number of imaging cycles, especially subsequent to vigorous mechanical agitation which can result in toner electroconductivity instability since, for example, the additives, such as carbon black, are not permanently retained on the surface of the toner. Additionally, several of the cold pressure fixing toner compositions of the prior art may have other disadvantages in some instances in that, for example, these compositions are obtained by processes which utilize organic solvents as diluents or as reaction media. The utilization of organic solvents renders the preparative process costly and potentially hazardous since most organic solvents are flammable and explosion-prone, and such processes also usually require expensive solvent separation and recovery steps. Moreover, the inclusion of solvents can also decrease the toner throughput yield per unit volume of reactor size. Furthermore, with many of the prior art processes toners of narrow size dispersity cannot be easily achieved as contrasted with the process of the present invention where narrow particle size distributions are generally obtained in embodiments thereof. In addition, many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse or shrinkage of toner particles during the toner work up and isolation processes resulting in a toner of very low bulk density. These disadvantages are substantially eliminated with the toners and processes of the present invention. More specifically, thus with the encapsulated toners of the present invention control of the toner physical properties of both the core and shell materials can be achieved. Specifically, with the encapsulated toners of the present invention in embodiments thereof undesirable leaching or loss of core components is avoided or minimized, and image ghosting is eliminated in many instances. Image ghosting is an undesirable phenomenon commonly encountered in ionographic printing when undesirable toner compositions are utilized. It refers, for example, to the repetitious printing of unwarranted images, and arises primarily from the contamination of the dielectric receiver by the unremovable toner materials. This problem can sometimes be partially eliminated by use of suitable surface release agents which aids in the removal of residual toner materials after image transfer. The toner compositions of the present invention eliminate or substantially eliminate the image ghosting problem by, for example, providing a polyether-urea shell which has a low permeability to the core components, thus effectively inhibiting their leakage to the toner surface, and preventing them from coming into contact with the dielectric receiver during the image transfix process. The shell materials of the present invention, with the aid of surface additives, also provides excellent surface release properties, thus enabling efficient removal of residual toner materials from the dielectric receiver surface. Furthermore, the excellent surface release properties afforded by the toner of the present invention can also dramatically enhance the image transfer efficiency of the transfix development processes.
In a patentability search report, the following prior art, all U.S. patents, were recited: U.S. Pat. No. 4,520,091 which discloses an encapsulated toner with a core of a colorant, a polymer, certain solvents, and an organic liquid with a boiling point in the range of 100.degree. to 250.degree. C., see for example the Abstract of the Disclosure; U.S. Pat. Nos. 4,642,281; 4,761,358 (see also column 5 wherein various shells are disclosed including polyureas); U.S. Pat. Nos. 4,780,390 and 4,784,930 (see also column 5 wherein shells composed of a complex layer of a polyurethane and a polyamide are disclosed, and at line 55, column 5, wherein there is recited the interfacial polymerization using a combination of a polyisocyanate and acid chloride, and polyamine), which disclose encapsulated toners with, for example, cores containing certain solvents, oily liquids, see for example column 3 of the '390 patent, in combination with a silicon; U.S. Pat. No. 4,581,312, see for example column 2, line 63, wherein a capsule toner comprising a core of a soft resin solution is recited; and U.S. Pat. Nos. 3,893,932; 4,296,192 and 4,803,144.
The following U.S. patents are mentioned: U.S. Pat. No. 3,967,962 which discloses a toner composition comprising a finely divided mixture comprising a colorant material and a polymeric material, which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2 and 3, 6 and 7, particularly lines 13 and 35, however, it does not appear that encapsulated toners are disclosed in this patent; U.S. Pat. No. 4,565,764 which discloses a microcapsule toner with a colored core material coated successively with a first resin wall and a second resin wall, reference for example the Abstract of the Disclosure and also note columns 2 to 7, and particularly column 7, beginning at line 31, wherein the first wall may comprise polyvinyl alcohol resins known in the art including polyurethanes, polyureas, and the like; U.S. Pat. No. 4,626,490 contains a similar teaching as the '764 patent and more specifically discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8, beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins, such as polyphenylene oxide or thioether resin, or mixtures thereof; and U.S. patents of background interest include U.S. Pat. Nos. 4,442,194; 4,465,755; 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions usually containing pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Interfacial polymerization processes are also described in British Patent Publication 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenylisocyanate, or toluene diisocyanate monomers. Also, the shell-forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which then react with unhydrolyzed isocyanate monomers to enable the formation of a polyurea microcapsule wall. Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydrides as a soft component.
Furthermore, other representative prior art, includes U.S. Pat. Nos. 4,254,201; 4,465,755, and Japanese Patent Publication 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell, which outer shell is preferably comprised of a polyurea resin. In the '201 patent there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the '755 patent discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the '201 patent there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Also, there are illustrated in U.S. Pat. No. 4,280,833 encapsulated materials prepared by interfacial polymerization in aqueous herbicidal compositions. More specifically, as indicated in column 4, beginning at line 9, there is disclosed a process for encapsulating the water immiscible material within the shell of the polyurea, a water immiscible organic phase which consists of a water immiscible material, that is the material to be encapsulated, and polymethyl polyphenyl isocyanate is added to the aqueous phase with agitation to form a dispersion of small droplets of the water immiscible phase within the aqueous phase; and thereafter, a polyfunctional amine is added with continuous agitation to the organic aqueous dispersion, reference column 4, lines 15 to 27. Also of interest is the disclosure in column 5, line 50, wherein the amine selected can be diethylene triamine, and the core material can be any liquid, oil, meltable solid or solvent soluble material, reference column 4, line 30. A similar teaching is present in U.S. Pat. No. 4,417,916.
In U.S. Pat. No. 4,599,271, the disclosure of which is totally incorporated herein by reference, there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate, and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
Other prior art includes U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, which illustrates an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamide, reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamide to produce the shell, see column 4, line 34.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. Further in U.S. Pat. No. 5,043,240 (D/89069), the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye; and thereover a polymeric shell, which contains a soft and flexible component, permitting, for example, proper packing of shell materials resulting in the formation of a high density shell structure, which can effectively contain the core binder and prevent its loss through diffusion and leaching process. The soft and flexible component in one embodiment is comprised of a polyether function. Specifically, in one embodiment there are disclosed in the aforementioned patent encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a shell preferably obtained by interfacial polymerization, which shell has incorporated therein a polyether structural moiety. Another specific embodiment of the patent is directed to encapsulated toners comprised of a core of polymer binder, pigment dye or mixtures thereof, and a polymeric shell of a polyether-incorporated polymer, such as a poly(ether urea), a poly(ether amide), a poly(ether ester), a poly(ether urethane), mixtures thereof, and the like. The aforementioned toners can be prepared by an interfacial/free-radical polymerization process involving dispersing a mixture of core monomers, colorants, free radical initiator, and one or more water-immiscible shell precursors into microdroplets in an aqueous medium containing a stabilizer. One of the shell precursors in this organic phase is a polyether-containing monomers or prepolymers. The nature and concentration of the stabilizer employed in the generation of stabilized microdroplets depend mainly, for example, on the toner components, the viscosity of the mixture, as well as on the desired toner particle size. The shell-forming interfacial polymerization is effected by addition of a water soluble shell monomer into the reaction medium. The water soluble shell monomer in the aqueous phase reacts with the water-immiscible shell precursors in the organic phase at the microdroplet/water interface resulting in the formation of a microcapsule shell around the microdroplet. The formation of core binder from the core monomers within the newly formed microcapsule can be subsequently initiated by heating, thus completing the formation of an encapsulated toner. The toner compositions of the present invention contain, for example, a nonvolatile liquid; a readily flowable core composition is employed; the ready flowability of the core composition ensures its rapid diffusion out of the ruptured toners and efficient fixing onto the paper substrate during the image fixing step. As a result, excellent image fix, and excellent image definition and visual quality can be obtained. Furthermore, with proper choice of the nonvolatile organic liquid for the core composition, excellent image transfer as well as clean image development are readily accomplished in some embodiments.
There is a need for encapsulated toner compositions with many, and in some embodiments substantially, if not all, the advantages illustrated herein. More specifically, there is a need for encapsulated toners with core comprised of a polymer binder, a nonvolatile organic liquid, and a magnetite, and thereover an impermeable shell that can contain the core components within the shell effectively. Also, there is a need for encapsulated toners wherein images with excellent definition and resolution, and superior fix are obtained. Moreover, there is a need for encapsulated toners, wherein image ghosting, toner offsetting, and undesirable leaching of core components and the like are avoided or minimized. Additionally, there is a need for encapsulated toners with in some instances, excellent surface release characteristics enabling their selection in imaging systems without silicone oils and the costly apparatus associated therewith. Furthermore, there is a need for encapsulated toners, including colored toners, which exhibit no toner agglomeration thus providing a long toner shelf life exceeding, for example, one to two years, and wherein the core is encapsulated in a shell comprised of a polyether-urea material. Also, there is a need for encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to render them relatively conductive enough to a volume resistivity level of preferably from about 1.times.10.sup.3 to 1.times.10.sup.8 ohm-cm, and to enable their use in single component inductive development systems. Further, there is a need for encapsulated toners wherein surface additives such as metal salts or metal salts of fatty acids and the like are utilized to primarily assist in toner surface release properties. There is also a need for processes for the preparation of encapsulated toners with many of the advantages illustrated herein. Specifically, there is a need for interfacial polymerization processes for encapsulated toner compositions, wherein the core contains a polymer binder, a nonvolatile organic liquid, and a magnetite. Furthermore, there is a need for toners and improved processes thereof that will enable the preparation of pressure fixable encapsulated toner compositions whose properties such as shell strength, core binder molecular weight and the nature of core binder crosslinking can be desirably controlled. Moreover, there is a need for enhanced flexibility in the design and selection of materials for the toner shell and core, and the control of the toner physical properties, such as bulk density, particle size, and size dispersity.